Information storage and retrieval system



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Original Filed Aug. 21, 1962 3E GQQ .3 Su QC Q2 352mm mmmmam 2758i 29 wk .6 #503 5 55 as t 50 Q H 7 Q2 mmumam awaits L V 29 i2 22 Q2 Qwbwmwmu mzQxxfiua F 22 NR2} :2 06.83% motwkmq \CRQQWG \tQxuGB BE meo moo v g2 -55 was QEE was 23mm w Elma Q\ 0F United States Patent Olhcc Re. 26,919 Reissued June 23, 1970 26,919 INFORMATION STORAGE AND RETRIEVAL SYSTEM David W. Hagelbarger and William G. Hall, Morris Township, Morris County, and William A. Malthaner, Colts Neck, N..I., assignors to Bell Telephone Laboratories, IYBCOlIPOIMed, New York, N.Y., a corporation of New or Original No. 3,242,470, dated Mar. 22, 1966, Ser. No. 218,271, Aug. 21, 1962. Application for reissue Mar. 29, 1967, Ser. No. 637,030

Int. Cl. 1104 3/14 US. Cl. 340-1725 32 Claims lVIatter enclosed in heavy brackets II] appears in the original patent but forms no part of this reissue specification; matter printed in italics indicates the additions made by reissue.

ABSTRACT OF THE DISCLOSURE An information retrieval system is disclosed wherein a plurality of operators obtain access on a time-sharing basis to a machine readable information storage file. To reduce the time required for searching through the file, indexing apparatus is provided whereby certain request information from the diflerent operators is compared on a character-by-character basis with index information to identify the general location of the requested information in the fig? If, for a specific request, this comparing operation ca not be completed because of insufiicient request information, the indexing apparatus is released to other operators for use by them until the particular inquiry in question is more fully specified. When access is restored and upon receipt and comparison of sufficient request information, a block of entries specified by the comparison is read out from the file and transmitted to the requesting operator for display on a cathode my viewing tube.

FIELD OF THE INVENTION This invention deals with the selective retrieval of desired units of information from mechanisms in which large amounts of such information are stored. Its principal objects are to provide rapid and positive access to the store, to share such access among a number of applicants for it, and to present to each applicant the information retrieved at his behest in convenient and immediately usable form.

DESCRIPTION OF THE PRIOR ART For satisfactory retrieval of a desired item of information from any mechanized library the initial storage of such information must have been carried out accord ing to some systematic plan; and the simpler the plan, the surcr is the retrieval. Provided that the information is of a character to lend itself to such treatment, arrangement of the items of information in numerical or alphabetical order is an advantageous plan to adopt, in which case any desired information may be recovered by merely scanning through the store, item by item, until the esired one is found. On the other hand, if the library be a large one, its mere magnitude poses problems of a different kind. If it is of such great bulk that the capital investment in the store itself is very considerable, the time required to carry out such a scanning process may be prohibitive, especially if a number of readers ask for service at the same time; and still more so if their demands are urgent.

An illustrative situation in which a number of operators require frequent and ready access to a large store of information that is alphabetically arranged is found in the modern Telephone Information Bureau. In New York city at the present time each of a number of diflFercnt bureaus is manned by some information operators, each of whom is provided with a library of telephone directories totaling pounds in weight. While the cfiiciency of thecs operators is high, the average time required to answer an inquiry is 36 seconds. Because of the ever greater number of subscribers to telephone service and their ever greater reliance on the information bureau, inquiries are received at the rate of some million per day. Obviously, the cost of maintaining such an operation is high and substantial economies would result from the installation of an automatic or semiautomatic information processing system.

SUMMARY OF THE INVENTION Accordingly, it is a specific object of the invention to introduce automation into a telephone information bureau.

To this end the entire telephone directory is transcribed, in digital code form, onto a suitable retentive medium. Each name, with the corresponding address and telephone number, constitutes a single item of the stored information and these items are stored in an alphabetical or numerical order corresponding to that in which they appear in the printed directory. The entire set of items and the store containing it is termed the main file. To minimize the time required for access to the main filc, index sotres are provided; advantageously, one or more of the discs of the group are set aside for the purpose. Advantageously, too, the index is graded: coarse and fine; coarse, finer, finest; first order, second order, third order, fourth order, and so on to the extent dictated by the fineness of resolution required and the complexity of apparatus that can be tolerated. For simplicity of illus tration, indiccs of two grades are provided. There is a first coarse index containing, for example, 200 words or partial words arranged alphabetically and numbered serially and there are, in addition, 200 fine indiccs each corresponding to a single entry of the coarse index and each, in turn, containing, for example, 50 longer words, similarly arranged, each accompanied by a numerical designation of the location, in the main file, at which the complete word appears.

The successive approaches by the control apparatus to the correct location in the main file are effected by successive interrogation of the indiccs with the name (or address) of the subscriber whose telephone number has been requested. The apparatus compares the inquiry, first with the successive items of the coarse index to identify a particular pair of fine indices and then, by comparison with the successive items of the selected fine indices to identify the word which most nearly resembles an item of the main file and to pick the location in the main file at which that item appears.

It is a feature of the invention that access to the main file is not sought until after this identification of the location in the main file has been successfully completed. It is another feature of the invention that the comparisons are made on a step-by-step basis, successful comparison with the coarse index leading at once to the identified fine index and successful comparison with that fine index leading at once to the desired location in the main file.

Once the correct location in the main file has been thus defined and picked, an entire block or batch of information items, cach an entire entry in the telephone directory, is read out of the main file into a buffer or buffers for further processing. This read-out can take place in a small fraction of a second, whereupon the main store is released for acceptance of read-out instructions originating with other operators.

The block of entries read out at the behest of a particular operator is next translated, first, from binary code into the form of alphabetical and numerical or alphanumeric" symbols and, then, from these symbols into video" signal form suitable for application to a conventional cathode ray viewing tube. Each operator of the group is provided with one such viewing tube onto the screen of which the block of information read out from the main file in response to that operators request, or a selected part of it, is presented in visually readable form.

As a refinement, in order to reduce eye strain and insure against errors of reading, only a fraction, for example, one eighth of the block of information read out of the main file is presented on the screen at one time and the selection of this fraction from the entire block is under the manual control of the operator who thus, figuratively, shifts a window over the block to expose a desired part of it. This is accomplished in the following way.

The video isgnal, into which the entire information block is convetred before application to the viewing tube, is stored on a spiral track of one of the discs of the set. Because the video signal is highly redundant as compared with the compact character of the coded information in the main file, the information block in its video form occupies several turns of the spiral track. The width of this track is determined by the magnetic transducer with which it is recorded on the face of the disc. In accordance with the invention, the width of the read-out transducer or "head is only a fraction, one fourth or one fifth. of the width of the recording transducer. Thus, the part of the record recovered by the read-out head lies entirely within a single turn of the spiral throughout three fourths or four fifths of a revolution of the disc which bears it. By adjustment of the radius, measured from the center of the shaft, at which the read-out head is located, and coordinated adjustment of the switching operations by which it is activated and deactivated, it cyclically and repeatedly reads out the video information stored at a particular part of this truck, being de-energized during the one fourth or one fifth of disc revolu tion in which the spiral line which separates each turn of the spiral track from its neighbor passes under the read-out head. Both the radial location of the read-out head and the switching times are together controlled by the operator seeking the information. Simultaneously and in response to the same control by the operator, the instant, during each scanning cycle of the viewing tube, at which the vertical sweep of the scanning beam commences is also determined. The result of this three-way control by the operator is to present the operators eyes a short list of some -20 items, each consisting of a name, an address and a telephone number, and ap=pear ing brightly in letters and numerals that may be one eighth-one fourth inch high. In case the item sought for does not appear in this list, the alphabetical arrangement of the list immediately informs the operator whether the desired item lies above the window or below it, in which case a further manipulation of the manual control in the proper direction brings it immediately into view.

The mechanism by which comparison is made between a specified item and the coarse and fine indices may take various forms. In one form the operator commences to type" the name (or address) of the party whose telephone number is requested on a keyboard instrument which delivers, for each key depressed, the corresponding binary digital code. As the symbols are typed, they are stored in a register and, character by character and commencing immediately the first character has been registered, the item or partial item, thus registered is compared on a numerical basis with all of the words of the coarse index. These may advantageously be stored in a single circular track of one of the discs and the comparison can be completed in a single disc revolution, i.e., in /{30 second. A counter determines how many of the partial words in the coarse index are identical with the partial item stored to date in the register, Evidently, the

smaller the number of characters registered, the greater the number of partial words in the coarse index that resemble it. Hence the count of identities starts with a large number and is successively reduced as the typing progresses. When the count indicates that the coarse index contains only one partial word that is identical with the partially typed inquiry, or none at all, switching operations are initiated which select a particular pair of fine index tracks identified by the number of the word in the coarse index thus picked; one lying just ahead of the coarse index word thus picked and the other just after it. From now on the comparison is made as before between the partial item as typed to date and the consecutive words of the two fine indices, the count of identities becoming progressively smaller. As before, when the count indicates only one identity, or none at all, similar switching operations are initiated which, this time, select a location in the main file; i.e., a particular disc of the set, one or the other of two sides of this disc, one of some 800 adjacent circular record tracks on this disc side and a sector of this track at which the code counterpart of the initial entry of the desired information block is stored. Read-out and presentation to the operator then take place as described above.

To insure that the information item required shall in fact be contained among the information items thus extracted from the main file, the extraction commences with a block of fifty items immediately preceding the point at which it is established that there is at least one identity or that there are no identities. In the case of an identity count of zero, the required item must be contained in this first block of fifty items and it is therefore arranged that the extraction shall go no further. In case a single identity has been encountered, the required item may be among the fifty items preceding the identity or among the fifty items which follow it and it is there fore arranged that the extraction continue through a second block of fifty items. In addition, and to cope with situations in which all of the information available in the operator has been registered and extraction is required despite the fact that it is still insuificient to define a location in the main file to a precision of one item in a hundred, provision is made to extract a still larger string of items, i.e., three, four or five sequential blocks of fifty. This exceptional extraction is initiated by a special signal, while the number of sequential blocks of fifty so extracted is automatically determined by the number of identities counted.

As a consequence of the character-by-character comparisons, full specification of the desired location in the main file may well have been achieved before the specification of the inquiry is complete, especially in the case of the less common names. This makes for a substant lal economy of the total time required for processing an lnquiry. Furthermore each interrogation of an index, coarse or fine, which does not identify a particular one of the index words causes immediate release of the access mechanism to other operators for use by them pend- 1ng the time at which the particular inquiry shall have been more fully specified by the addition of one or more characters. Thereupon, access is restored to the particular operator for a further attempt.

It is another feature of this character-by-character registration of the inquiry, that, when access is restored to an operator who is in the course of building up the specification of an inquiry, the outcome of comparisons previously made is retained so that they need not be repeated.

In an alternative embodiment which utilizes no keyed codewriter and relieves the operator of the typing burden. the coarse alphabet is initially displayed on the screen of the operators viewing tube. For this purpose it may be stored as a video signal for direct application to the viewing tube. The operator is provided with a stylus equipped with a photocell in its tip. The operator merely touches the viewing screen at the point bearing the partial word of the course index which most nearly resembles the name for which inquiry has been made. As the cathode beam passes this point, the output signal of the photocell marks the fractional time, within the scanning cycle at which this occurs, thus identifying the line of characters constituting the selected partial word. This registered time acts to select a particular one of the 100 or so fine indices which, along with its fellows, has been stored in the same form as the coarse index, and to present it in its entirety on the screen of the viewing tube. Again, the operator merely touches the screen with the photosensitive stylus at the point bearing the name most nearly resembling the name for which inquiry has been made. As before, this acts to register the time, within the scanning cycle, at which the cathode beam passes this point, and the time thus registered identifies a location in the main file at which the required information block is recorded. Read-out and presentation take place as before.

Because of the rapidity with which each of the foregoing operations takes place, a large number of them, like or unlike, and originating with different Operators, can take place on a time-division basis within a brief time interval. Thus all the apparatus components of the system, with the exception of a few that must of necessity be individual to the operator are shared by a number of operators.

The invention will be fully apprehended from the following detailed description of an illustrative embodiment taken in connection with the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, all components shown in the various portions of FIG. 1 are assigned reference characters in series 101499; all those shown in FIGS. 2A2E are assigned reference characters in the series 201-499 and so on. The first digit of any reference character thus guides the reader to the principal figure in which it is shown. In many cases the same component is also shown in another figure where it is identified by another reference numeral, of which the last two digits are the same. Especially in the case of input conductors and output conductors which are common to two or more figures, a reference character is in certain cases shown in one figure in parentheses. This reference character, by virtue of its position in the number series, guides the reader to another figure in which it also appears.

In the drawings:

FIG. 1 is a block diagram showing the major features of an embodiment of the invention in broad outline;

FIGS. 2A, 2B 25, arranged as shown in FIG. 3, together constitute a block schematic diagram showing apparatus embodying the invention;

FIG. 4 is an outline diagram showing a spiral record track of substantial width and a portion of a single turn of the spiral to which a transducer of substantially less width responds;

FIG. 5 is a block schematic diagram showing vertical sweep and window-control apparatus for selectively locating the transducer-actuating portion of the spiral track of FIG. 4;

FIG. 6 is a block schematic diagram showing a word comparator including a number of individual character comparators;

FIG. 7 is a block schematic diagram showing the structure of any of the character comparators of FIG. 5;

FIG. 8 is a block schematic diagram showing the access-obtaining portions of an alternative embodiment of the invention;

FIG. 9 is a block schematic diagram showing apparatus including a name file and an address file and means for coordinating information simultaneously retrieved from both files;

FIG. 10 is a block schematic diagram illustrating apparatus for the automatic generation of indices; and

6 FIG. 11 is a block schematic diagram showing a modification of FIG. 2B and affording increased flexibility.

The following table of contents will be of assistance to the reader in his perusal of the detailed description which ensues.

Detailed Description TABLE OF CONTENTS Column Outline 6 The main file 7 Read-out 8 Digital buffer and frequency standardization 8 Code translation and symbol generation 9 Conversion to video signal and display 9 The video store 10 Window control 11 Indices of main file and access mechanism-First embodiment 13 The word comparator 18 Individual operator's location registers 22 Clearing of registers 23 Indices of main file and access mechanism-Second embodiment 24 The address file and its uses 25 Numbers most frequently and least frequently called for 26 Emergeny lists -c 27 Design and updating of indices 28 Interlacing; parallel processing 30 Outline Referring now to the drawings, FIG. 1 shows the major features of one embodiment of the invention in broad outline. The heart of the system is the man file 101 which, along with other apparatus components shown in the upper part of the figure, is accessible in common, and on a time-division basis, to a number of individual operators. The apparatus individual to one of such operators is shown in the lower prt of the figure. Switches 150,

151 indicate accessibility to other operators.

The main file 101 contains, in binary code form, all of the thousands of information items of which a telephone directory is composed. Each item consists of a subscribers name, his address, and his telephone number. The individual items are systematically arranged: in alphabetical order of names, in numerical order of addresses, or both. Each item is stored at a specific location; since the item occupies space, the location is that of the first character of the item. Insertion of the items is accomplished by well known means, here indicated, simply, write-in and updating circuits 102.

With a costly main file, access time is at a premium. Hence searching the main file to locate a desired item is to be avoided. Instead, an index 116, preferably graded into at least two layers, is provided, through which, in response to interrogation by an operator, the location in the main file is determined at which a block of items containing the desired one commences. Thereupon the entire block is read out of the main file, processed, decoded, and converted by apparatus 104 broadly designated as serving these purposes. The resulting video signal is stored, for cyclic read-out and display, in the individual operators video buffer store 114. The display takes place on the screen of the operators individual viewing tube 111 and the items displayed comprise a subblock of a conveniently smaller number of items. By manipulation of a window control unit 115 the operator rapidly causes this subblock of items to progress, forward or backward, through the entire block read out, until the desired item appears among those of the subblock displayed.

The operator may then read the item and answer the inquiry. As a refinement, the operator may also be an action of the simplest kind, and with the air of an item identifier 161, identify the particular item sought. Such identifications, originating with all the operators of the group, are gathered by a statistical accumulator 166, and this controls the Write-in circuits 102, to inject into the main file, and adjacent each item requested, a marginal note" signifying the fact of the request. From such data lists can be constructed of items that are inquired for with exceptionally high, or low, frequency.

To obtain access the operator, by typing the name of the subscriber on a keyboard, inserts this name, character by character, and in binary code, in a register 121. Each time a new character is thus registered, the partial name consisting of the characters registered to date is transferred to a temporary store 127, and the partial word in the store is consecutively matched by a comparator 133 against the binary coded words of the index 116. Initially, the comparison is with the words of a coarse index that ranges through the entire alphabet, to identify the most nearly similar index word and so to make a selection from a number of fine indices. If the coarse comparison is successful, as determined by a decision element 136, a fine index is selected, and the character-by-character comparison proceeds as before for the later characters registered, to identify the main file location of the block of items appropriate for extraction.

To the contrary if, at any stage of the matching process, the registered word is insufficiently well defined to justify proceeding to the next step, the decision element 136, by a control path 135, clears the temporary store 127 and releases the access-obtaining apparatus to another operator who may in the interim have registered the name of another subscriber as to whom information is sought, with sufificient particularity to justify proceeding.

All of these operations take place on a rapid fire basis: thirty independent index comparisons can be made in a second of time. Hence an operator who, after some initial matching failures, may have registered a name with sufiicient particularity to make for success, is unaware of the many intervening comparisons with names registered by other operators.

For efficient operation of the system the index or indices must be well designed and well constructed. Moreover, as the information in the main file 101 changes from day to day, the indices 116 must from time to time be regenerated. The invention provides an index generator 152. fully described below, which insures congruence between main file and index and, at the same time, excludes from the index all information not actually helpful.

The main file In the main file 101, each entry may be standardized at fifty characters of which the normal telephone number occupies seven, and the normal address occupies from six to twelve, leaving some thirty characters, which is ample, for the name and for spaces of various lengths. For the sake of the certainty of operation which it provides, storage is in the form of binary code. One or more binary digits or bits out of a possible 6 can be arranged in 64 different ways. Accordingly, a 6-bit code provides for the coding of 64 different symbols; i.e., more than enough for all the letters of the alphabet, the Arabic numerals through 9, spaces of various lengths, punctuation marks and, if desired, a few signaling symbols.

Because of the readiness with which new entries may be inserted in the tile and old ones altered or erased, magnetic storage is preferred. For the sake of compactness, the store may take the form of a set of discs, each magnetizablc on both sides, mounted on a common rotary shaft. A set of 24 such discs, each 39 inches in diameter, and bearing on each side a magnetizable band 12 inches in width, each provided with several transducers mounted on a radially movable arm for write-in and read-out, is manufactured and sold by Bryant Computer Products Division. Ex-Cell-O Corporation. A single such set is sufficient for a community such as Atlanta, Georgia. A store three times as large, conveniently three sets of such 8 discs, would be required for a city of the size of New York City.

The fineness of the magnetic surface is such that individual circular record tracks may be spaced apart radially by less than 0.02 inch, and the bits may be packed to a density of better than 250 to the linear inch of track. Because more bits can be packed into an outer track than into an inner one, the sensitive surface may advantageously be divided into 6 annular zones, each 2 inches in width and containing 128 tracks. Fixed timing marks may be placed in the spaces between zones, each governing the bit packing in an adjacent zone. Information may be written into any track of any disc by conventional apparatus, here designated as write-in and updating circuits 102. For optimum utilization of storage space the write-in operation may be conducted at the appropriate one of six different frequencies spaced apart on the freguency scale in direct proportion to the mean radius of the zone containing the track in which the information is to be written. The entire assembly is rotated at a speed of 30 revolutions per second by a main drive.

Read-out The procedure for obtaining access to the main file at a desired location and the apparatus by which it is instrumented will be best understood in the context of the entire system as shown in FIGS. 2A 2E, arranged as shown in FIG. 3. For this reason the description of the access-obtaining parts of the apparatus will be postponed until after the remainder of the system has been described in broad outline.

Assume that one of a number of operators, whose individual consoles 203-1 through 203N are shown as indicated at the left-hand portion of FIG. 28 has, in answer to an inquiry, sought and obtained access to the main file 201 (FIG. 2E) at the location at which a block of entries embracing the one sought for is recorded. The entire block is read out by conventional means in the course of a few revolutions of the discs of which the main file is composed and, in most cases, in the course of a single revolution.

Digital buffer and frequency standardization To facilitate further processing and, in particular, in order that the processing bit rates for the several bits of each single entry may be alike, it is advantageous that their magnetic records be placed, in the main file 201 at identical radii from the central shaft. To secure this result the six bits of each entry will have been recorded on six different tracks on six different disc sides. The bit frequency of the read-out differs from each such group of six tracks of the main file 201 to the next. The six magnetic records of a single entry are first read out as six parallel streams of pulses, at a speed dependent on the radius at which they appear, into a digital buffer store 204 (FIG. 2E) into which they are written, at the same speed, on six contiguous tracks of a single disc, one or more discs of the set having been reserved for the purpose. Frequencies may then be standardized in well known fashion, i.e., by writing each stream of pulses thus recorded in one part of the buffer 204 into a shift register Without speed change and then reading the pulses out of the shift registers and writing them into another portion of the buffer 204 under the control of a clock; i.e., at a standard frequency. and with a standard spacing between each item and the next. Clock pulses for the purpose may conveniently be permanent marks on one of the discs so as to recur in the exact synchronism with the shaft rotation. The terminal 205 of the main file 201 carries synchronizing signals for this and many other purposes.

In most cases, a block of one hundred consecutive entries will more than sufiice, and these can be written into six single-turn tracks of the discs of the buffer store 204. Under some circumstances, a larger block, e.g., a block of 200-300 consecutive entries, may be needed. These will require several sets of six-track groups, and additional switching, not shown but of a type well known, can be provided to start the write-in of the second set when the tracks of the first set have been filled.

Code translation and symbol generation The block of entries now in the digital buffer store 204 is still in the form of 6-bit code. The code for each symbol is now translated by a decoder 206 into the specification of a single one out of 2, in this case 2 :64, possible conductors. The conductors of this set are connected to the several input points of a symbol generator 207 which, in turn, converts the specification of this conductor into signals representative of alphanumeric symbols, one for each code group of six bits. This symbol generator may take various forms, among them a rectangular array of magnetizable cores arranged in rows and columns, e.g., eight rows and seven columns, and threaded by wires of three kinds: row wires, column wires and a symbol wire. Core arrays of this type are utilized as character generators in Gordon et a]. Patent 2,920,312 and in W. J. Rueger Patent No. 2,820,956. The symbol generation may be carried out in various Ways, of which that employed by Rueger is preferred; i.e., the symbol wire which threads only those cores of the array that are arranged in the pattern of a specified symbol constitutes the input terminal of the symbol generator and is connected, as indicated in FIG. 2E, to a corresponding one of the 2 output conductors of the decoder. Read-out takes place, in response to the application of pulses derived in well known fashion from fixed marks on one of the discs to the column conductors in sequence, from all the row conductors simultaneously. This response consists, on each such row conductor, of one or more pulses, or none at all, one for each of the cores through which all three wires are threaded.

Conversion to video signal, and display The pulses on the several row conductors of the symbol generator 207 are now applied to a parallel-to-series converter 208 whose function is to rearrange them into video signal form. The converter 208 may be a delay line having a plurality of lateral taps, to which the individual row conductors are connected, and a single output terminal 209 at which the resulting video signal is developed. Equally well, it can be a part of one of the circular tracks on a disc, with which is aligned a single read-out head and a number of write-in heads, all spaced apart to provide the required differential retardations. This Video signal is selectively passed by a distributor 210 to the console 203-1 assigned to the operator requesting it for ultimate display on the viewing screen of the cathode ray tube 211 that forms part of that operators console (FIG. 2B). This tube may be of conventional construction and may be actuated in accordance with a conventional scanning program, i.e., 30 vertical sweeps per second developed by a generator 212 each containing some 200-300 horizontal sweeps developed by a generator 213 (FIG. 2A).

The horizontal sweep generator 213 is common to the display tubes 211 of all of the consoles 203 and hence causes the horizontal sweeps of the beams of all of these tubes to move in synchronism and in phase coincidence. Its operations are controlled by synchronizing signals derived from the terminal 205 of the main file 201 (FIG. 2B) so that the horizontal sweeps are not only synchronous with each other but are also in synchronism and in a fixed phase relation with the rotation of the discs of the main file and of hte digital buffer store.

The vertical sweeps of the beams of the several viewing tubes 211 (FIG. 2B) also take place synchronously with the rotation of the discs but, for reasons that will appear below, the phase relation between disc rotation and vertical sweep is advantageously controllable, for each of the viewing tubes 211, by the operator to whom it is assigned. Hence each console is provided with its own vertical sweep generator 212. The frequency at which each one operates is under control of synchronizing signals derived from the main file terminal 205 but the phase of its output wave, and hence of the vertical sweep, is individually controlled in the fashion to be described below.

To build up a visible display of the symbols represented by the video signal on the viewing screen requires that the uppermost portions of all of the symbols of a single 50 character entry, represented by the video signal derived from the top row conductor of the core array of the symbol generator 207 (FIG. 2E) be generated on one horizontal scan while the next lower portions, represented by the signals from the second row conductor of the core array, be generated on the following horizontal scan. Hence the delay interposed by the parallelto-series converter 208 (FIG. 2E) between each of its in ut taps or write-in heads and the next is equal to the time occupied by a single horizontal scan. This period is evidentl equal to the reciprocal of the number of scans per second, namely, 6000-9000, and the time required to build up an entire information item on the screen of the veiwing tube is eight times as long. It is to provide time in which this buildup can take place that, following the initial read-out from the main file into the buffer store, the shift register was called upon to standardize the spacing among entries.

Immediately read-out from the core array of the symbol generator 207 has taken place for the first symbol, it is desirable that the array be released for the generation of the next symbol. Provided the information thus read out is not lost track of, the release may readily be effected in conventional fashion, if necessary, by the application of reset pulses to the row wires.

The video store To preserve the information thus read out in video form for application to the operators viewing tube 211, it is first forwarded by the distributor 210 (FIG. 2E) to the particular operator requesting it and then placed in that operators video buffer store 214 (FIG. 2B) for cyclic read-out. To simplify or avoid problems of synchronization, this video store, together with those assigned to other operators, may advantageously be constituted of one or more discs of the set, On the same shaft as the main file and the digital buffer store and rotated synchronously with them. However, because of the high redundancy that characterizes a video signal, a block of 50 to entries, in video signal form, would occupy several full circular tracks. To prevent discontinuities and to provide further advantageous results that will be recognized from what follows, the video store is constituted of a spiral track. At normal rates and with normal packing densities, a block of 50 entries may occupy from 3 to 5 full turns of such a spiral while a block of 250 such entries may occupy 17-25 turns. Accordingly, the video signal output of the parallel-toseries converter 208 is applied to a transducer that is advanced by a lead screw juxtaposed with the sensitive face of the disc that is set aside to serve as the video store and the lead screw pitch and rotation speed are selected to cause the transducer head to advance radially, in the course of the rotation of the disc, thus to record the video signal along a spiral track.

FIG. 4 shows a portion of such a spiral track record. The width W of this track is several times as great as that of any of the circular tracks of the main file 201, and a fixed read-out head of width d that is only one fifth as wide as the track can still operate to read the information out of the track in unambiguous fashion. As the disc bearing the stored video signal on its spiral track rotates, the narrow read-out head lies entirely within a single turn of the spiral throughout V5 of a revolu- 11 tion. Given that the read-out head is actuated throughout this period in which track boundaries do not cross it and deactivated throughout the remaining fraction of each revolution of the disc, the video signal that is thus read out, cyclically and at 30 times per second, is constituted of only a portion of the entire information block written into it from the main file store; i.e., if the block occupies 7 turns of the spiral track, the fraction thus cyclically read out, in the case of a read-out head of /s, the track width, is

Vs rT or about 12% and. the greater the number of spiral turns occupied by the block, the smaller the fraction thus cyclically read out. The video signal thus cyclically read out acts to establish a path through a switch 218 (P16. 2B), theretofore open, and is then applied through this switch to modulate the intensity of the cathode beam of the viewing tube 211, i.e., to turn the beam on and OH, the beam having theretofore been blanked. Since, as indicated by the application to the horizontal sweep generator 213 (FIG. 2A) of synchronizing signals derived from the central timing source, e.g., from the terminal 205, horizontal scanning of the beam across the face of the viewing tube takes place in synchronism and in phase with other operations of the system, notably the rotations of all the discs, the characters thus built up on the tube face in the course of the scanning operarion are correctly located laterally, i.e., the first letter of each surname of a telephone subscriber appears at the lefthand margin of the viewing screen.

Window control A block of a few hundredindeed a block of fifty consecutive items that may have been read out from the main file is a large number for visual inspection without excessive eye fatigue. The much smaller number of entries cyclically read out of the video store 214 is quite otherwise. Individual symbols may be one-quarter inch high and spaced apart in the vertical dimension by another quarter inch, and each single group of fifty characters constituting an entry may extend from side to side of the viewing screen. This greatly facilitates visual selection by the operator of a single one of such entries thus presented to the eyes.

With video signals derived from magnetic cores in a rectangular array of seven columns and eight rows of which the symbol generator 207 is composed, the display on the screen of the viewing tube 211 is constituted of eight sequential horizontal scans for each character and hence for each index word or information item. To provide a character height of one quarter inch and a vertical spacing between entries of another quarter inch requires only that the adjacent horizontal scans be ,4, inch apart and that each group of eight be separated from the next by an abrupt vertical displacement of one quarter inch. The active sloping portion of the wave delivered by the vertical sweep generator 212 should therefore be broken by abrupt rises at the proper points. Means are Well known for generating a wave of this character.

Because of the restriction of the sublist of entries thus presented on the viewing screen to a fraction of the block read out, the individual entry sought for may not be among the items of this sublist. But because of the alphabetical or numerical ordering of the items in the main file 201 and consequently in the video store 215, the operator can easily recognize at a glance whether the indi vidual item sought for precedes the sublist presented or follows it. The operator thus knows what is called for to bring it into view; i.e., if the item sought for precedes the list presented, to move the list downward across the face of thetube or, if the item sought for follows the list presented, to move the list upward.

To accomplish this movement the operator is provided with a manual window control unit 215 of which the instrumentation will be described in further detail below.

12 In response to a single, simple manual operation, this window control unit does three things:

(a) By rotating a lead screw it moves the read-out head of the video store 214 radially inward or outward.

(b) It alters the instants in the rotation cycles of the disc at which the read-out head is activated and deactivated, retaining the duty cycle of four fifths.

(c) It trips the vertical sweep generator 212, which controls the vertical movements of the cathode beam so that each vertical sweep commences at the instant at which the readout head lies entirely within one turn of the spiral track (FIG. 4) and continues until it is about to leave that turn and pick up information from the adjacent turn.

In consequence, the operators manipulation of this control unit 215 causes the list of entries presented to the eyes to move upward or downward across the viewing screen as called for by the direction of the movement. Even an inexperienced operator provided with this arrangement can, in a short time, shift the sublist of displayed items vertically across the viewing screen until the individual item sought for appears among them. It is to be noted that it need only appear, and need not be centered. Hence, exactitude is not called for in the operation.

FIG. 5 illustrates one of many alternative arrangements for the instrumentation of the operators window control unit 215. A train of pulses of fixed frequency and standard reference phase derived, for example, from a fixed mark located on one of the rotating discs of the main file 201, is converted into a sine wave of the same frequency and phase by a low-pass filter 501 tuned to 30 cycles per second. A manually adjustable Phase shifter 503, operated by a manual crank 505, or an equivalent lever, shifts the phase of this sine wave to any desired extent. The output wave is converted by conventional apparatus combination of clipper 507, ditferentiator 509 and rectifier 511 into a train of unipolar pulses each of which acts to trip a sawtooth wave generator 513, causing it to commence its sweep. The generator 513 may be proportioned, in conventional fashion, to develop a sawtooth wave of which the voltage rises linearly with time to a certain point and then falls more abruptly. This is additively combined with a staircase wave developed by a generator 515 that operates in synchronism with the horizontal sweep generator 213 to develop the required composite wave of vertical risers and sloping steps. Successive cycles of this composite wave are app ied to the vertical deflection elements of the operators cathode ray viewing tube 21.1, thus to control the vertical scan of the cathode beam. The rising portions of the wave control the scan during the display while the falling portions govern the vertical flyback of the beam.

The sawtooth wave thus developed by the generator 513 is passed through a differentiator 517 which converts it into a square wave 519 of which the positive portions endure for /5 of each cycle while the negative portions endure for 6. The square wave is transmitted to the video bufier store, there to enable a conduction path extending from the read-out head juxtaposed with the spiral track (FIG. 4) of the video store 214 to the control electrode of the viewing tube 211, the positive portions of the wave serving to establish the path while the negative portions disestablish it. Thus the passage of signals from the head is fully coordinated in frequency and in phase with the vertical sweep of the cathode beam of the tube 211..

The manual control 505 which actuates the adjustable phase shifter 503 acts, e.g., through a synchrotransmission link of which the transmitter 525 and electrical transmission path 523 are shown, and of which the receiver is located physically with the video store 214, to rotate a lead screw that carries the readout head. A gear box, not shown may be interposed to coordinate the rotation angle of the lead screw, which of course 

